astronomy chapter 15 and 16

bright, sphere-shaped region of stars that occupies the central few thousand light-yeras of the milky way galaxy?

galaxy's bulge

gas and dust that lies between the stars in the milky way galaxy

interstellar medium

two small galaxies that orbit the milky way galaxy

magellanic clouds

it is the continuous recycling of gas in the galactic disk between stars and the interstellar medium

star-gas-star cycle

elements heavier than hydrogen and helium constitute about ? of the mass of the milky way's interstellar medium

2%

subatomic particles that travel close to the speed of light

cosmic rays

which of the following molecules is the most abundant in molecular clouds

H2

interstellar dust consists mostly of

microscopic particles of carbon and silicon

a cloud of hydrogen and helium that contracts to become a galaxy

protogalactic galaxy

most stars in the milky way galaxy are ?

very old

a colorful cloud of gas that glows because it is heated by light from nearby hot stars

ionization nebula

the most common form of gas in the disk of the milky way galaxy

atomic hydrogen gas

all of the following types of objects are found almost exclusively in the disk (rather than the halo) of the milky way except

globular clusters

what law of nature explains why the galaxy began to rotate rapidly and flattened out as it shrunk in size

law of conservation of angular momentum

the circular but relatively flat portion of the galaxy is the ?

disk

the first portion of the galaxy to form was the ?

halo

a tightly packed group of a few hundred thousand very old stars is a ?

globular cluster

a ? stands out in a photo of a galaxy because it shines brightly with light from massive young stars and glowing clouds of gas and dust

spiral arm

stars orbiting in the ? near the galaxy's center can have orbits highly inclined to the galactic plane

bulge

estimated number of galaxies in our observable universe

100 billion

not one of the major categories of galaxies

globular clusters

a light source of known luminosity

standard candle

a type of very luminous star that makes an excellent standard candle

cepheid variable

the more distant a galaxy, the faster it is moving away from us

hubble law

the "boundary" of our observable universe

the cosmological horizon

cosmological redshift is the result of ?

the expansion of the universe

current estimated place the age of the universe at about ?

14 billion years

telescopes designed to study the earliest stages in galactic lives should be optimized for observations in

infrared light

collisions of galaxies typically unfold over a period of ?

hundreds of millions of years

the unusually bright centers found in some galaxies

active galactic nuclei

an active galactic nucleus that is particularly bright

quasar

the mass of a supermassive black hole thought to power a typical bright active galactic nucleus is roughly ?

1 billion solar masses

what does the cosmological redshift do to light?

stretches its wavelength

suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum

a spiral galaxy

first link

radar

second link

parallax

what baseline distance must we know before we can measure parallax

the earth-sun distance

standard candle techniques

cepheids, white dwarf supernovae, main sequence fitting

which technique is most useful for measuring the distance to a galaxy located 10 million light years away

cepheids

hubbles law expresses a relationship between ?

distance of the galaxy and speed at which it is moving away from us

our sun belongs to the ? if the milky way galaxy

disk component

the globular cluster M13 belongs to the ? of the milky way galaxy

spheroidal component

a ? contains hot, ionized gas but very little cool gas or dust

elliptical galaxy

the milky way is a ?

spiral galaxy

the type of galaxy known as a ? was more common in the universe 10 billion years ago

irregular galaxy

scientists investigating ? study how the distribution of galaxies changes with time

cosmology

? have the highest rates of star formation

starburst galaxy

the largest individual galaxies in the universe are known as ?

central dominant galaxies

the collective activity of many supernova events in a relatively small volume of a galaxy can create ?

galactic winds

the energy for all active galactic nuclei is thought to come from in-fall of matter in ?

supermassive black holes

often characterized by sources of immense energy located hundreds of thousands of light years away on either side of their centers

radio galaxies

astronomers measure the AU with this technique in which radio waves are transmitted from earth and bounced off venus

radar ranging

allows us to determine (with about 10%) a cepheid's luminosity simply by measuring the time period over which its brightness varies

period-luminosity relation

Hubble's constant

H0

the idea that the universe has no center or edge, and on large scales looks about the same everywhere

cosmological principle

a galaxy's type might be determined in part by the rotation of the protogalactic-cloud system from which it formed.

protogalactic rotation

a galaxy's type might be also be determined in part by the density of the protogalactic clouds from which it formed

protogalactic density

long ? of plasma connect to the lobes to the very center of the galaxy, where we find an active galactic nucleus that is firing the jets of plasma outward at speed that can be close to the speed of light

jets

an expanding shell of hot, ionized gas driven by stellar winds of supernovae, with very and very low density gas inside

bubble

electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms

21 centimeter line

tiny, solid flecks or carbon and silicon minerals that resemble particles of smoke and form in the winds of red giant stars

dust grains

theoretical models suggest that the spiral pattern of star formation is caused by disturbances called ? that propagate through the gaseous disk of a spiral galaxy like the milky way

spiral density waves

consists of stars that follow the orderly orbital patterns of the disk (sometimes called population 1)

disk population

consists of stars that orbit the center of the galaxy with many different inclinations, so that they cross through the disk during their orbits (sometimes called population 2)

halo population